1. Technical Field:
This invention relates to methods of forming structural and mechanical parts from fiber-reinforced ceramic matrix composite (FRCMC) materials, and more particularly, to the compression and injection molding of these parts.
2. Background Art:
Composite material structures are very popular for various uses. Typically, these structures constitute a matrix of "cured" organic resins with some type of fiber dispersed throughout. More recently, fiber reinforced ceramic matrix composite (FRCMC) structures have been made available for use where due to high temperatures organic composites are not suitable. A typical FRCMC structure comprises fibers of various types and lengths disposed throughout a ceramic material formed from a pre-ceramic resin. While organic composites will burn readily, FRCMC, being a ceramic, withstands heats that can destroy even metals. For example, a FRCMC material can withstand continuous temperatures up to about 1000.degree. F., cyclical temperatures up to about 2000.degree. F., and short-term exposure to temperatures up to about 3500.degree. F.
FRCMC structures are made by combining the aforementioned pre-ceramic polymer resin, such as silicon-carboxyl resin sold by Allied Signal under the trademark BLACKGLAS or alumina silicate resin (commercially available through Applied Poleramics under the product description CO2), with fibers. Examples of types of fibers which might be employed include alumina, Altex, Nextel 312, Nextel 440, Nextel 510, Nextel 550, silicon nitride, silicon carbide, HPZ, graphite, carbon, or peat. These fibers can be supplied in rigid or binderized preforms, woven or braided preforms, random mat preforms, fabric, tow (thread), or chopped tow or fabric. The resin-fiber mixture is formed into the shape of the desired structure and heated for a time to a temperature, as specified by the material suppliers (typically between 1,500.degree. F. and 2,000.degree. F.), which causes the resin to convert into a ceramic material.
There are many methods which can be used to form the FRCMC structures. For example, a resin transfer molding (RTM) process is described in a co-pending application entitled METHODS AND APPARATUS FOR MAKING CERAMIC MATRIX COMPOSITE LINED AUTOMOBILE PARTS AND FIBER REINFORCED CERAMIC MATRIX COMPOSITE AUTOMOBILE PARTS by the inventors herein and assigned to the common assignee of the present application. This co-pending application was filed on Aug. 16, 1995 and assigned serial number 08/515,849. The RTM method described in the co-pending application generally involves forming a preform in the shape of the part from the aforementioned fibers; placing the preform in a cavity of a mold having the shape of the part; forcing a liquid pre-ceramic polymer resin through the cavity to fill the cavity and saturate the preform; heating the mold at a temperature and for a time associated with the pre-ceramic polymer resin which transforms the liquid pre-ceramic polymer resin-saturated preform into a polymer composite part; removing the polymer composite part from the mold; and, firing the polymer composite part in a controlled atmosphere at a temperature and for a time associated with the pre-ceramic polymer which transforms it into a ceramic, whereby the polymer composite part is transformed into a fiber reinforced ceramic matrix composite part.
The RTM method of forming FRCMC structures works well for its intended purpose. However, this method requires the use of a fiber preform which must be placed in the mold prior to the structure being formed. These preforms add to the expense of producing the FRCMC structure, not only due to the cost of the preform itself, but also because of the extra processing steps required to install the preform into the mold.
Accordingly, there is a need for a method of making FRCMC parts that is conducive to mass producing these parts at a faster pace and at a reduced cost in comparison to other methods, such as RTM processes.
Wherefore, it is an object of the present invention to provide such a method of making FRCMC parts via a compression molding process wherein instead of having to employ fiber preforms such as with a RTM process, chopped fibers are mixed with a pre-ceramic resin prior to placing the mixture into a compression mold.
Wherefore, it is another object of the present invention to provide such a method of making FRCMC parts via an injection molding process wherein instead of having to employ fiber preforms such as with a RTM process, chopped fibers are mixed with a pre-ceramic resin prior to being injected into an injection mold.
It is also an object of the present invention to provide such a method of making FRCMC parts having heterogeneous structures wherein various portions of the part included different fiber types and potentially different filler materials which impart characteristics desired to be exhibited by a particular portion of the part.